1. Field of the Invention:
This invention relates to the area of liquid chromatography and specifically to continuous detection of viscosity of column effluent in such systems.
2. Description of the Prior Art
Liquid chromatography pertains to a particular variety of equipment and techniques for analyzing the components of an unknown sample of liquid material.
Liquid chromatography is a process wherein a sample having unknown components is forced to migrate through an elongated "column." The column contains a material held statically inside it, called a "stationary phase." The stationary phase is chosen for its ability to selectively retain the various potential components of the sample with which it comes in contact with differing degrees of tenacity. The sample is forced to migrate through the column by injecting it into a solvent upstream of the column and subsequently pumping the solvent and dissolved sample through the column.
When the dissolved sample is forced through the column, each of its components migrates through the column in a particular time related pattern, which pattern is a function of the degree of the tendency of the stationary phase to retain that component.
Some properties of the column effluent are affected by the concentration of sample in the emergent fluid. One of the properties which may be affected is the viscosity of the effluent. By detecting variations in this property of the effluent, and plotting these variations against time, certain information can be derived as to the nature and amount of the components in the sample.
For example, for predetermined column conditions and flow rate, it may be known that a particular hypothetical component, if present in the sample, will reach a maximum concentration in the column effluent at a specific time following introduction of the sample to the column. This time is known as the "retention time" of the component. This phenomenon occurs because of the existence of the particular degree of retention of that component by the stationary phase. By measuring a property of the effluent known to be affected by the hypothetical component, and observing whether a maximum occurs at the "retention time" for that component, presence of the component can be verified or negated.
It is evident that in liquid chromatography there exists a necessity for accurately detecting and measuring, on a continuous basis, properties of the liquid emerging from the column, such as viscosity.
It is known in liquid chromatography to measure many properties of the column effluent to derive information relating to the nature and quantity of the components in a sample. Among the properties measured are visible light and ultraviolet ray absorption, refractive index, heat of absorption and flame ionization of the sample.